The present invention relates to release control of a physiologically active substance, more specifically to an electroresponsive hydrogel and a physiologically active substance release control system comprising a biosensor (particularly a biosensor comprising an enzyme-immobilized ion sensitive field effect transistor), an amplifier and an electroresponsive hydrogel containing a physilogically active substance.
For example, in the treatment of diabetes mellitus, it is considered desirable to release insulin into blood according to blood sugar level for maintenance of the level in a particular range, irrespective of food intake time and food consumption. In general, a mode for physiologically active substance administration capable of releasing an essential physiologically active component in a necessary amount according to changes in physiological conditions in vivo (hereinafter referred to as "physiologically active substance release control system") is useful for the treatment of various diseases.
As insulin pumps, there have been developed, for example, portable infusion pumps such as the MILL-HILL injector (Harvard Apparatus) and implantable administration systems such as the sophisticated, telemetry-modulated implantable infusion pump (John Hopkins University). However, these insulin pumps allow continuous release of a given amount of insulin at a constant rate, and cannot release an essential physiologically active substance in a necessary amount according to changes in physiological conditions in vivo.
Also, there are many reports on biosensors that convert chemical information in vivo to electric signals, but studies of carriers suitable to the controlled storage and release of the desired physiologically active substance should be made for the realization of release control of a physiologically active substance by means of these biosensors.
With a potential for use in these applications, hydrogel, which shows expansion-contraction changes in response to external stimulation such as light, temperature, pH or electric field, has recently drawn much attention. For example, drug release could be reportedly controlled using a temperature-sensitive gel [You Han Bae et al.: Makromol. Chem. Rapid Commun., 8, 481 (1987)]. Also, Tanaka et al. [Science, 218, 467 (1982)] reported an electroresponsive hydrogel for the first time.
However, any configuration of release control system characterized by its temperature-based drug release control is considered as of little practical value because it is difficult to control the system due to temperature control, etc. when used in human bodies, etc. In addition, it remains unknown what is an optimal configuration for practical use of an electroresponsive hydrogel. With this background, there are demands for development of a release control system which can serve for practical use and a hydrogel which can serve as a component thereof.